In wireless communication systems, base stations are traditionally equipped with a small number of antennas. A radically different approach involves base stations with an unprecedented numbers of antennas (M) simultaneously serving a much smaller number of mobile terminals (K where M>>K) using multi-user beamforming. Operating with a large ratio of antennas to terminals under simultaneous service can yield large increases in both spectral efficiency and energy efficiency. As the number of service antennas increases and power is reduced the most simple signal processing, conjugate beamforming on the forward link and matched-filtering on the reverse link, asymptotically achieves near-optimal performance.
One technical challenge associated with large antenna array (LSAS) networks is access (e.g., timing acquisition, cell search, paging, etc.), particularly if the base station power is significantly reduced compared to conventional base stations. The LSAS base stations typically do not know the channel state information for terminals, and this makes achieving a reasonable closed-loop beam forming gain difficult. As a result, convention push-based broadcast operations, such as broadcasting system and timing synchronization information (also called cell search), paging, etc., do not fit well with low power LSAS based networks.